May 2002

From American Physical Society

Physics tip sheet #13 -- May 15, 2002

1) Fusion in the round
M. E. Cuneo, et al.
Physical Review Letters (Print issue: May 27, 2002)

Achieving inertial confinement fusion (ICF) has been a goal of the US fusion program for 25 years. Imploding a small capsule of frozen deuterium-tritium fuel may allow ignition of a fusion reaction that would produce a usable excess of energy. However, considerable technical challenges face the project including creating a fast enough implosion that is uniform in all directions to within a few percent. This is now looking feasible based on the latest experiments using the Z-pinch x-ray machine at Sandia National Laboratory (in collaboration with Los Alamos and Lawrence Livermore National Labs). Experiments show that the system should be able to uniformly and sufficiently compress the larger fusion capsules (>5mm) required for high fusion yields.

Journal article:

2) Neutrinos make for small extra dimensions
H. Davoudias, P. Langacker and M. Perelstein
Physical Review D (Print issue: May 15, 2002)

Fundamental theories of particle physics and cosmology often require the use of extra dimensions that might be "curled up" to small scales. The existence of oscillating neutrinos (as recently confirmed by Sudbury Neutrino Observatory data) places constraints on how large any extra dimensions could be. Using the latest neutrino data, the authors' most conservative bound suggests that extra dimension should only be visible on a scale less than 0.82 micrometers (approx. one millionth of a meter). Thus, currently planned gravitational experiments are unlikely to detect these dimensions if they exist.

Journal article:

3) Nuclear pasta
G. Watanabe, K. Sato, K. Yasuoka, T. Ebisuzaki
arXiv preprint server

The formation of neutron stars from collapsing supernovae are some of the most dramatic processes in stellar evolution. In a neutron star, high densities cause matter to form a uniform liquid but just before that happens, nuclei form rod-like and slab-like structures and bubbles, termed nuclear "pasta". The existence of pasta phases change the dynamics of neutron stars and how they behave astrophysically. New detailed simulations have shown how hot nucleic matter can form the various pasta phases as it cools. The matter seems to pass through a series of phases starting from uniform matter and heading through spherical, cylinder-like, slab-like phases and then as more uniform matter with holes that are cylindrical and then spherical before the whole lot becomes uniform again at a lower temperature.


4) Electron liquid crystals
L. Radzihovsky and A. T. Dorsey
Physical Review Letters (Print issue: May 27, 2002)

Electrons don't normally know one direction from another, so researchers were perplexed a few years ago when they found a cold plane of electrons suddenly choosing to conduct many times better in one direction than in the perpendicular one. Maybe they could acquire a preferred orientation by acting like liquid crystals, theorists proposed. Now a group reports it has worked this theory out well enough that experimenters may finally have some detailed signs to search for.

Physical Review Focus:
Journal article:

5) Chromium atoms on demand
S. B. Hill, J. J. McClelland
APS Division of Atomic, Molecular, and Optical Physics meeting (May 28-June 1, 2002)

A NIST group can now supply chromium atoms on demand, one at a time, the first time such control over neutral atom delivery has been achieved.

Physics News Update:
Meeting abstract:

6) How fit are the surviving fittest?
E. M. Rauch, H. Sayama, and Y. Bar-Yam
Physical Review Letters (Print issue: June 3, 2002)

Darwin's great idea of "survival of the fittest" is well accepted in evolutionary circles but how do you define fittest? A common way is in terms of the number of surviving offspring per organism. However, models have shown that it is possible for a species with high reproduction rates to dominate in the short term but die out over a longer timescale (~200 generations) due to depletion of resources. This paper looks at a new definition of long-term fitness by taking into account that descendents may have different reproductive success than their ancestors. One conclusion is that different species are adapted to survive over different time scales and that this leads to a different range of surviving species than if selection worked only at one time scale.

Journal article:

7) Evaporating black holes to pin down the Higgs boson
Y. Uehara
arXiv preprint server

A number of authors have suggested that microscopic black holes may be produced in the next generation of particle colliders currently being planned and built. Now one physicist has claimed that among the residues as the microscopic black holes evaporate should be Higgs bosons and that only one month of running time of the Large Hadron Collider (LHC) should be sufficient to determine one property, the spin, of the Higgs boson.

Preprint: (Spin of Higgs boson)
Background journal article: (Creation of black holes at LHC)

This article comes from Science Blog. Copyright 2004

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